1. Field of the Invention
The present invention generally relates to an in-line multicylinder combustion engine for use primarily in motorcycles and, more particularly, to provide the in-line multicylinder combustion engine of a kind that is assembled compact in size with its center of gravity lowered and that a relatively large banking angle can be obtained when such combustion engine is mounted on a motorcycle.
2. Description of the Prior Art
An in-line multicylinder internal combustion engine of a large engine displacement that is mounted on motorcycles has a substantial weight and, accordingly, efforts have been made to render the motorcycle as a whole to have a lower center of gravity by installing a crankshaft at a relatively low position such that the combustion engine has a lower center of gravity. In the in-line multicylinder combustion engine of the type referred to above, the combustion engine has a relatively large width because multiple engine cylinders are arranged in-line, that is, because the multiple engine cylinders are laid transverse relative to a motorcycle frame structure, and, accordingly, where an electric generator, generally known as dynamo, is disposed on one end of the crankshaft that is positioned in a lower region of the combustion engine, the lower region of the combustion engine tends to exhibit an increased width.
Also, it is well known that if a cylinder bore is designed to be large in size and a piston stroke is also designed to be short, the combustion engine can provide a high rotational speed, hence a large drive output. However, the larger the cylinder bore, the greater the total width of the combustion engine. Accordingly, considering also that the electric generator is disposed on one end of the crankshaft as discussed above, it is difficult to obtain a relatively large banking angle of the motorcycle frame structure. As a result thereof, increase of the size of the cylinder bores is difficult to achieve.
On the other hand, the Japanese Laid-open Publication No. 58-065936, for example, discloses an in-line multicylinder combustion engine of a design in which an electric generator is disposed not on one end of the crankshaft but at a rear side of an engine cylinder. According to this known design, the total width of the combustion engine can advantageously be reduced as compared with that of the engine design in which the electric generator is disposed on one end of the crankshaft and, accordingly, a relatively large banking angle of the motorcycle can be obtained.
However, where the crankshaft is arranged in line with input and output shafts as shown in FIG. 1 of the above discussed patent publication, it has been found that not only does the front-to-rear length or the longitudinal dimension of the combustion engine become great along with increase in weight thereof, but a wheelbase of the motorcycle also increases, resulting in an undesirable increase of the size and weight of the motorcycle.
Also, where the crankshaft and the output shaft are arranged level relative to each other with the input shaft positioned below them, the length of the combustion engine can be reduced, but the positioning of the crankshaft above the input shaft requires the electric generator, drivingly coupled with the crankshaft by means of a generally endless belt, to be positioned above the input shaft, shifting the center of gravity of the combustion engine to a higher position. With this design, setteing the center of gravity of the combustion engine at a lower position is difficult to achieve.